It is known to use supercritical conditions for the treatment of organic waste in a water based liquid or liquefied substance in order to separate out solids and extract combustible gases, in particular methane. Such processes typically use an oxidising agent to oxidise the organic material under supercritical conditions, for instance as described in U.S. Pat. No. 4,822,497, U.S. Pat. No. 5,543,057 and JP2004131560. One of the known problems of known processes is the depositing of inorganic salts in the interior surface of the pressurized chamber in which the supercritical conditions are present. The use of a fluidized bed helps to reduce the deposits on the internal walls of the reaction chamber on the one hand by encouraging the deposit of salts on the grains of the fluidized bed and on the other hand by the abrasive effect on the grains against the internal wall of the reactor as described in U.S. Pat. No. 5,543,057.
In U.S. Pat. No. 5,543,057, as in other processes requiring an oxidizing reaction, a portion of the thermal energy contributing to the transformation from a subcritical to a supercritical condition is provided by the oxidation reaction. As the composition of the wet biomass may vary significantly, the control of this process may not always be optimal and thus the control of the transition from subcritical to supercritical temperatures may also not be well controlled. This can lead to unwanted deposits in portions of the reactor. Moreover, there are processes in which it is not desirable to have an oxidisation agent either for cost reasons, or because of the chemical properties of the water based solution to be treated.
In processes for the precipitation of solids in a fluidized bed reaction chamber, despite the presence of the fluidized bed with its abrasive effect to reduce deposits forming on the reaction chamber in a wall, certain portions in the reaction chamber may not be optimally circulated, thus allowing the deposit of salts on the walls, for instance at the inlet of the reaction chamber.